We plan to determine the level of control of the expression of RNA tumor virus genes in transformed (nonmalignant) mammalian cells. Preliminary evidence indicates that at least a portion of the oncogenic viral genome persists in the DNA of infected cells that have reverted to the normal phenotypes suggesting that the phenomena of reversion is a function of regulation of genetic expression of the viral genes responsible for transformation. Studies will be conducted to determine whether the entire viral genome is present in the revertant cell and the location of the viral DNA.